A. Field of the Invention
This invention relates to the field of particle beams. More particularly, the present invention relates to the control of particle beams by modifying the size, divergence, direction, mean kinetic energy, and kinetic energy distribution of said particle beams. Even more specifically, the present invention addresses the extraction and deceleration of antiprotons from a synchrotron.
B. Background of the Invention
Charged particle beams are typically accelerated in linear accelerators, cyclotrons, or synchrotrons. It is often desirable to extract some or all of these charged particles and to transport them at a kinetic energy lower than the beam energy just prior to extraction. For example, a synchrotron can be used to decelerate a charged particle beam. One option pursued in synchrotrons has been to use a curved silicon crystal to guide the particles out of the accelerator and simultaneously lower the beam energy via collisions with the electrons in the crystal material. See, for example, R. A. Carrigan Jr., G. P. Jackson, et al, “Extraction from TeV-Range Accelerator using Bent Crystal Channeling”, Nucl. Instr. and Methods in Phys. Research B90, 128 (1994); C. T. Murphy, G. P. Jackson, et al, “First Results from Bent Crystal Extraction at the Fermilab Tevatron”, Nucl. Instr. and Methods in Phys. Research B119, 231 (1996); A. Assev, G. P. Jackson, et al, “First Observation of Luminosity—Driven Extraction using Channeling with a Bent Crystal”, Physical Review Letters—Special Topics: Accelerators and Beams Vol. 1, 022801 (1998); and R. A. Carrigan Jr., G. P. Jackson, et al, “Beam Extraction Studies at 900 GeV using a Channeling Crystal”, Physical Review Special Topics: Accelerators and Beams Vol. 5, 043501 (2002). A second option has been to use a dipole switch magnet to steer the beam into the desired transport channel, or transfer line. See, for example, Y. K Tai, et. al., “Neutron Yields from Thick targets Bombarded by 18- to 32- MeV Protons”, Phys. Rev. Vol.109, No.6, p.2086 (1958). For example, proton therapy treatment centers use dipole switch magnets to steer the beam between a number of patient treatment rooms, as in U.S. Pat. No. 4,870,287, which is incorporated by reference. Depending on the application, there is sometimes a block of material embedded in a transport channel to decelerate the particles to lower kinetic energies, again through collisions with the electrons in the material. See, for example, D. H. Perkins, “Introduction to High Energy Physics”, 4th Ed., (Cambridge University Press, 2000), p.349.
A third option, generally utilized in synchrotrons, involves fast-risetime “kicker” bending magnets to deflect the particles down an alternative beam transport channel. See, for example, A. Faltens and M. Giesch, “Fast Kicker Magnets for the 200 GeV Accelerator”, IEEE Trans. Nucl. Sci., p.468, June 1967. The junction between this extraction channel and the rest of the accelerator is typically the site of a Lambertson magnet, which introduces an additional bending magnetic field in either the extraction channel or along the accelerator trajectory. See, for example, M. P. May, G. W. Foster, G. P. Jackson, and J. T. Volk, “The Design and Construction of the Permanent Magnet Lambertson for the Recycler Ring at Fermilab”, Proc. U.S. Part. Acc. Conf., p.3280 (1997). The use of Lambertson magnets have been established in previous patents, such as U.S. Pat. No. 4,870,287, which is incorporated by reference. It is only after this Lambertson magnet use that a block of material is imposed into the path of the particles and energy reduction or “degrading” is accomplished.
When a charge particle travels through a block of material, a reduction in kinetic energy occurs because of collisions with the electrons in the material For example, such degraders are routinely used to set the dose depth during cancer therapy with protons, as in U.S. Pat. No. 6,034,377, which is incorporated here by reference. See also, for example, Y. Jongen, et. al., “Process Report on the Construction of the Northest Proton Therapy Center (NPTC) Equipment”, Proc. U.S. Part. Acc. Conf., p.3816 (1997); E. Pedroni, et. al., “A Novel Gantry for Proton Therapy at the Paul Scherrer Institute”, CP600, Cyclotrons and Their Applications 2001, Sixteenth International Conference, edited by F. Marti (2001, American Institute of Physics 0-7354-0044-X), p.13; and A. Yamaguchi, et. al., “A Compact Proton Accelerator System for Cancer Therapy”, Prc. U.S. Part. Acc. Conf., p.3828 (1997).
Another embodiment of such a degrader is described in U.S. Pat. No. 6,433,336, which is also incorporated by reference. Unfortunately, at the same time the charged particles also endure collisions with the nuclei within the material. See, e.g., D. H. Perkins. These nuclear collisions cause the particles of the beam to disappear or scatter into a rapidly diverging cloud. For this reason degraders tend to be thin and have specialized optics surrounding them that are more tolerant of the increased beam divergence.
The focusing or converging of charged particle beams is generally accomplished with magnetic lenses that generate either a quadrupole field transverse to the direction of beam travel, solenoid magnets that generate a uniform magnetic field in the direction of beam travel, or lenses which are composed of an electric current flowing with the beam. Quadrupole and solenoid magnets have been used for decades to modify the size and divergence of charge particle beams. See, for example, E.Courant & H. Snyder, Annals of Physics, vol. 3, p.1 (1958). For example, these types of converging magnets are used to focus proton beams onto cancer therapy patients, as described in U.S. Pat. No. 6,034,377, already incorporated by reference.
There are two classes on focusing lenses that are formed by an electric current that flows coincidently with the charged particle beam. The first is another charged particle beam that travels through vacuum concurrently inside the beam that is to be focused. See, for example, G. Jackson, “Tune Spectra in the Tevatron Collider”, Proc. U.S. Part. Acc. Conf., p.861 (1989);N. Solyak, et. al., “Electron Beam System for the Tevatron Electron Lens”, Proc. U.S. Part. Acc. Conf., p.1420 (2001). The other class of lens passes an electric current through a solid, liquid, or ionized gas or plasma while the charged particle beam is simultaneously passing through the material. See respectively, for example, S. O'Day and K. Anderson, “Electromagnetic, Thermal and Structural Analysis of the Fermilab Antiproton Source Lithium Collection Lens”, Proc. U.S. Part. Acc. Conf. (1995); A. Hassanein, et. al., “The Design of a Liquid Lithium Lens for a Muon Collider”, Proc. U.S. Part. Acc. Conf., p.3062 (1999); G. Hnimpetinn, et. al., “Experimental Demonstration of Plasma Lens Focusing”, Proc. U.S. Part. Acc. Conf., p.3543 (1993).
There are two ideas for a system in which any two of the degrading, steering, and focusing functions are simultaneously implemented. The first is the use of a lithium lens to simultaneously focus and decelerated muon beams. See, for example, A. Hassanein, et. al. This idea is believed to be purely theoretical and no one has shown a way to actually make and use this idea. The second idea is to use magnetization of shielding steel in particle physics calorimeters in order to bend secondary particles that emanated from an atom-smashing event. In this case, the charged particles are in an amorphous cloud, and not in a classical charged particle beam.
One of the uses of degraded charged particle beams is their storage and transportation in containers. For example, a Penning trap can be used to transport antiprotons, as described in U.S. Pat. No. 6,576,916 B2 and incorporated here by reference.